Method of inserting buttons in a drilling head

ABSTRACT

A button and sleeve have matching tapers and are pressed together so that in a working configuration the external diameter of the sleeve is stretched to slightly exceed the diameter of the bore into which the combined assembly is to be inserted. The sleeve is then partially removed from the button to relax its external diameter so that the combined assembly can be placed into the bore. The bit and sleeve are then pressed into the working configuration in the bore until the sleeve has expanded radially into tight contact with the inner wall of the bore and the button has seated itself on the end wall of the bore. A button and sleeve assembly are pressed together and have matching surfaces which cause the exterior dimension of the sleeve to exceed that of the bore into which the assembly is to be inserted when the button and sleeve are combined together in a working configuration. The sleeve and button matched surfaces, however, are dimensioned to allow the external dimension of the sleeve to shrink to a dimension less than the inner dimension of the bore when the sleeve is partially removed from the button.

Write tates atent 1191 Pearson Dec. 10, 1974 METHOD OF INSERTING BUTTONS IN A DRILLING HEAD [75] Inventor: Bernard A. Pearson,- Bothell, Wash. [73] Assignee: Smith-Williston, Inc., Seattle, Wash. [22] Filed: Dec. 10, 1973 [21] Appl. No.: 423,259

Related US. Application Data [60] Division of Ser. No. 303,334, Nov. 3, 1972, which is a continuation-in-part of Ser. No. 232,695, March 8, 1972, abandoned.

[52] US. Cl 29/525,29/526, 175/410, I 175/413 [51] Int. Cl B23p 19/02 [58] Field of Search 29/525, 526; 76/107 A; 175/410, 413, 374; 403/276, 277, 282, 284

[56] References Cited UNITED STATES PATENTS 2,146,995 2/1939 Simons 76/107 A 2,466,546 4/1949 Huelster..... 29/525 UX 2,899,672 8/1959 Lewis. 29/525 UX 3,101,934 8/1963 Poundstone 175/410 X 3,537,539 11/1970 Adcock 1 175/413 3,551,981 1/1971 Hagar 29/525 X 3,618,683, 11/1971 Hughes 175/410 3,693,736 I 9/1972 Gardner 175/410 3,749,190 7/1973 Shipman 29/525 X FOREIGN PATENTS OR APPLICATIONS 494,597 10/1938 Great Britain 29/525 Primary Examiner-Charlie T. Moon Attorney, Agent, or Firm-Seed, Berry, Vernon & Baynham [5 7] ABSTRACT A button and sleeve have matching tapers and are pressed together so that in a working configuration the external diameter of the sleeve is stretched to slightly exceed the diameter of the bore into which the combined assembly is to be inserted. The sleeve is then partially removed from the button to relax its external diameter so that the combined assembly can be placed into the bore. The bit and sleeve are then pressed into the working configuration in the bore until the sleeve has expanded radially into tight contact with the inner wall of the bore and the button has seated itself on the end wall of the bore.

A button and sleeve assembly are pressed together and have matching surfaces which cause the exterior dimension of the sleeve to exceed that of the bore into which the assembly is to be inserted when the button and sleeve are combined together in a working configuration. The sleeve and button matched surfaces, however, are dimensioned to allow the external dimension of the sleeve to shrink to a dimension less than the inner dimension of the bore when the sleeve is partially removed from the button.

19 Claims, 10 Drawing Figures METHOD OF INSERTING BUTTONS IN A DRILLING HEAD CROSS REFERENCE TO RELATED APPLICATION This is a divisionof application Ser. No. 303,334, filed Nov. 3, 1972 which in turn is a continuation-inpart of application Ser. No. 232,695, filed Mar. 8, 1972, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to button and sleeve assemblies for rock drill heads or the like and to methods of installing the combined button and sleeve assembly in a head.

2. Description of the Prior Art As stated in my earlier application, one of the problems with prior art rock drilling heads is that the but tons in many cases are not replaceable resulting in the necessity of replacing the entire head at a cost of several times the cost of the individual button when only a few bits are actually in need of replacement. One prior art attempt at providing replaceable buttons was unsuccessful since the buttons were difficult to remove, often became loose, and in some cases caused cracking of the head under percussive loading. This prior art technique employed buttons mounted in sleeves which were fitted in bores in the head assembly. These sleeves were split so that they expanded against the inside wall of the bores. The bores were provided of necessity with an internal central opening accessible from the interior of the head assembly so that a worn sleeve and button could be driven out from within. The placement of the buttons in the head was thus primarily determined by the availability of access from within the head to drive out the buttons and was not designed for optimum drilling configurations. Furthermore, the necessity of numerous access holes weakened the structure of the head assembly. Still further, the sleeves did not firmly hold the button in the head and under percussive loading the buttons would become loosened or broken.

Other prior art attempts at replacing the buttons without the use of sleeves have proven extremely expensive since the buttons are difficult to machine to the exact tolerances of the bores in the head and often fractured the metal around the bore when being pressed into the bore. In addition, the percussive loading on the buttons is transmitted directly to the edges of the bores, causing damage of the edges and requiring that a bore be recut to a larger size before a replacement button can be installed. Furthermore, the replacement bottom is then an odd size making it expensive to manufacture.

SUMMARY OF THE INVENTION It is an object of this invention to provide a button and sleeve assembly comprising a bit and a sleeve which can be manufactured and stored as an integral unit and adapted for installation in various size holes in a rock drill head-or the like.

Basically, the button' and sleeve assembly comprises a button having an outer surface and a sleeve having a matching inner surface such that when combined in a working configuration the exterior dimension of the sleeve is stretched to exceed the inner dimension of the opening in which the button and sleeve assembly are to be inserted. Working configuration for the purposes of this description means a button pressed within a sleeve to the same extent as when finally pressed into the opening in the head. The matching surfaces are dimensioned such that upon partial removal of the sleeve from the button the exterior surface of the sleeve is reduced to a dimension less than the dimension of the opening. This configuration allows a button and sleeve assembly to be accurately formed to a desired external dimension and thus be matched to the dimension of a hole in a drill head. Thus the bit button and sleeve can be stored in a partially disassembled (but not completely) condition and can then be inserted into the opening of the drill head and pressed into the working configuration such that the sleeve will be expanded into tight engagement between the button and the sidewall of the opening. r

The method of this invention comprises forming a bore in a drilling head with an inner end wall, combin- 'ing a button and a sleeve into a working configuration with the button within the sleeve, forming the conbined bit and sleeve while in said working configuration to reduce the external dimensions of the sleeve, moving the button and sleeve slightly relative to each other to reduce the external dimension of the sleeve and button, placing the bit and sleeve into the opening, and then moving the button and sleeve relative to each other to expand the sleeve radially until the button and sleeve are returned to their combined working configuration with the sleeve being pressed tightly against the button and the bore. I v I i In the preferred form the button and sleeve have matching tapers with the taper of the sleeve diverging toward the end wall of the bore and the step of moving the button and sleeve into the bore includes the step of first seating the button against the end wall of the bore and then pressing the sleeve over the button also into engagement with the end wall of the bore. The preferred method also includes the step of maintaining the button and sleeve in the exact same rotational alignment with each other'during pressing into the cylindrical bore as when they are pressed together into said normal working configuration. In this mannerthe irregularities in the shape of the button are compensated for by the deformation of the sleeve and this exact compensation is not changed since the sleeve and button are never rotated relative to one another'again during the remainder of the installation procedure. Also in the preferred form the taperis made in the sleeve by first cold forming it over a die and combined with the button in its working configuration the exterior surface of the sleeve is ground to be slightly greater than the diameter of the bore.

As is apparent, the sleeve serves as a protection for the edge of the hole since percussive loading on the button will damage the sleeve rather than the edge'of the hole which is less deformable than the sleeve. The sleeve expands against the sidewall of the bore by radial expansion and does not cause gouging or overstressing of any portion of the bore. Furthermore, the entire surface of the hole is expanded uniformlywithout overstretching the entrance to the bore so as to hold the sleeve tightly in the bore. Since the sleeve is expanded uniformly against the bore it holds the button securely and reduces the chance of breakage of the button. The button can be easily removed by cutting the sleeve from around the button to free the bit in the hole.

Another advantage is that the button can remain at its standard production size and the sleeve made oversized to recover a drilling head having an oversized hole caused from prior damage to the hole. In prior art devices such-a head was often discarded at a tremendous cost merelyv because the cost of machining a carbide button to the configuration of the oversized hole was too expensive. Still another advantages is that since the end of the button abuts directly against the end wall of the bore in the drill .head rather than against the sleeve as in the prior art, the sleeve can be made much thinner thus reducing the size of the hole and increasing the strength of the head and allowing an increased number of buttons in the head.

Still further the invention is equally applicable for replacement of buttons in existing conventional drilling heads or as an original manufacturing technique for new drilling heads. It is particularly advantageously employed as a technique for mounting the buttons in drilling heads receiving high loading such as those used in tunnel boring machines and the like. Not only are the buttons more easily installed by this invention but the buttons are held more securely and thus the drilling head and the buttons last longer for such severe drilling applications.

In the preferredembodiment the sleeve receives a pressure during installation rather than the button thus allowing greater flexibility in the hardness of the button. As a result a wider range of customers specifications for button composition can be maintained.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an environmental view of a typical drilling head showing a button and sleeve assembly embodying the principles of this invention and installe according to the methods of this invention.

FIGS. 2A-2G are schematic operational views illustrating various steps in the method of installation which embody the principles of this invention. FIG. 2C, for example, specifically shows a typical button and sleeve assembly in a working configuration prior'to being installed in the rock drilling head. FIG. 2 D specifically shows a technique for storing the combined button and sleeve prior to installation in the drilling head. FIG. 2F illustrates a typical installation of a button and sleeve assembly in a drilling head.

FIG. 3 illustrates an alternative'method step for removing the sleeve when a button is to be replaced.

FIG. 4 illustrates an alternative form of button and sleeve assembly, the installation of which is basically the same as that shown in the steps illustrated in FIGS. 2A-3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS sembly for use in a drilling head, and methods of installing button and sleeve assemblies in the drilling head. This application discloses additional subject matter incorporating improvements of the originally disclosed installation method and expands on the description of I a preferred installation method. For this purpose, FIG. 2A illustrates a technique for cold forming a taper on a sleeve 44. Preferably the sleeve is madefrom 4340 low alloy steel and is coined on a die 80 using conventional cold forming practices. The tapered sleeve is then heat treated to 38-40.

In the preferred form, a typical sleeve will initially have an outer diameter slightly greater than the diameter of the bore in the drilling head to which the sleeve will finally be inserted. The cold forming step on the die provides the internal taper of the sleeve with diameters of about 0.005 of an inch less than the corresponding top and bottom diameters of the carbide button 42 with the button having a taper of 0.20 of an inch diameter per inch of sleeve length formed during sintering of the buttons. In a typical example, a bit is composed of 9 V2 to 10 A percent cobalt carbide of tungsten of the type manufactured by Diamond Metal Alloys. The composition of the sleeve and button will vary to some extent, however, due to the requirements of the user of the drill head. A typical drilling head can be made from Bethlehem Steel Corporation tool steel ASTM Grade 7, sold under the trademark Bearcat.

In FIG. 2B the now tapered sleeve 44 is positioned over the corresponding button 42 and in FIG. 2C forced down over the button for an interference fit of 0002-0004 inch using a pressure of approximately 10,000 pounds. The dimensions illustrated in the figures, are intended toshow a typical example only it being understood that buttons and sleeves may vary in size depending on the users requirements. FIG. 2C illustrates a working configuration" of the combined button and sleeve and is identical to the configuration they will assume when placed within a bore'of the drilling head. While in this working configuration, .the circumference of the sleeve is machined or preferably ground to reduce its diameter to a diameter slightly in excess of the internal diameter of the bore 60 in the drilling head to allow a 0.0030.0035 press fit.'Several sizes will be made to allow for off size bores in the drilling head.

FIG. 2D illustrated a button and sleeve in a storage position with the sleeve slightly retracted from the button 42. While not necessary to practicing the invention, it has been found desirable to store the sleeve on its corresponding button. In this way the sleeve is never removed, and thus its angular orientation with respect to the button is not lost. This provides the advantage of perfect mating between the internal surface of the sleeve and the external surface of the button caused by the 10,000 pounds pressing force illustrated'in step 2C. All irregularities in the button become compensated for by the ductile material in the sleeve. Rotation of one of the members relative to the other would of course destroy this perfect uniformfit. In the position shown in 2D the sleeve is also permitted to relax sufficiently so that its external diameter becomes less than the internal diameter of the bore60.

FIG. 2E illustrates the step of placing the combined button and sleeve in the bore 60 and applying a pressure of 24,000 pounds to force the sleeve over the button into its working configuration shown in FIG. 2F. The button is first placed against a seat in the bore which may be an insert in the bore or as illustrated the end wall of the bore. The guide 72 supports the sleeve as it is being forced over the button 42. As shown in exaggerated form-in 2E, the small gap between the external diameter of the sleeve 44 and the internal diameter of the button 42 allows the sleeve to be moved relative to the button a substantial distance before the radially outer edge of the sleeve begins to contact the sidewall produce a hardness of about R of the bore 60. Expansion of the diameter of the sleeve is primarily radially so that when it reaches its final working configuration in 2F, there is a uniform application of force pressing outwardly against the entire inside wall of the bore 60. The outer edge of the bore is thus not subjected to stretching and results in a tight fit at the outer end of the bore. The sleeve extends outwardly beyond the bore protecting the edge of the bore from abrasive or percussive forces. The button is seated on the inner wall 62 of the bore and thus transmits loads directly to the drilling head to better transfer the percussive loads between the button and the head.

FIGS. 2G and FIG. 3 illustrate two methods of removing the button and sleeve from the bore 60. In FIG. 2G a rotary cutting tool 73 is employed to cut the sleeve from between the button and the sidewall of the bore thus freeing the button for removal. In FIG. 3 an electrode 90 of an electric discharge machine, well known in the art, is employed to erode the sleeve from between the button and sidewall of the bore by theuse of an electric charge.

FIG. 4 illustrates another embodiment of the sleeve and button assembly. In this embodiment a bit 100 is employed with a converging external taper similar in angularity to the taper of the preferred embodiment. The button is fixed within a sleeve 101 of a material similar to that of thepreferred'ernbodiment. In this form of the invention, a button and sleeve will be formed in a working configuration such as that shown in FIG. 2C and stored as in FIG. 2D. Insertion of the button and sleeve into the bore 60 occurs first by seating the sleeve 101 against the end wall of the bore or a suitable insert and finally pressing the button into the sleeve to expand the sleeve against the sidewall of the bore 60. The button is illustrated in a position where it is initially inserted into the bore with an exaggerated gap between the sidewall of the sleeve and that of the bore fror the purposes of description.

While preferred forms of the invention have been illustrated and described it should be understood that alternatives and modifications will be apparent to one skilled in the art without departing from the principles of the invention. Accordingly, the invention is not to be limited to the specific embodiments described.

The embodiments of the invention in which a particular property or privilege is claimed are defined as follows: I Y

l.'A method of installing and holding an externally tapered button in a cylindrical bore in a drilling head by means of an internally tapered .metal expansion sleeve, comprising;

forming the sleeve with its outer surface oversized relative to the sidewall surface of the bore and with its inside surface generally the same shape as the tapered outer surface of the button and undersized relative thereto,

axially pressing the sleeve and button together into a normal working relationship and, while in said relationship, shaping the outer surface of the sleeve to generally the same shape as the sidewall surface of the bore and to a size that is oversized relative to said sidewall surface while the sleeve and button are fully pressed together and that is undersized relative to said sidewall surface when the sleeve is in a relaxed state,

less than fully pressed together, moving the button and sleeve relative to one another sufficiently to permit the sleeve to shrink to said undersize whereat its outer surface is small enough to permit the sleeve to enter the bore without interference and then pressing the button and internally tapered metal sleeve together in the cylindrical bore until the sleeve is elastically expanded by the button tightly between the button and the sidewall surface of the bore.

2. The method of claim 1, said cylindrical bore having an inner seat said internally tapered metal sleeve being annular and having a generally cylindrical outer surface, said step of pressing the button and sleeve together in the bore including abutting the button against said inner seat.

3. The method of claim 2, said seat including an inner end wall of the bore, the taper of said sleeve inner surface converging toward the end wall of the cylindrical bore and said step of pressing the button and sleeve together in the cylindrical bore including first pressing until the sleeve rests against the end wall of the bore and second pressing until the button rests against the end wall of the bore. I

4. Themethod-of claim 2, said seat including an end wall of the bore, said taper of said sleeve inner surface diverging toward the end wall of the cylindrical bore and said step of pressing the button and sleeve together in the cylindrical bore including first pressing until the button rest aggainst the end wall of the bore and second pressing until the sleeve rests against the end wall of the bore.

5. The method of claim 1 wherein said button and sleeve are in the same exact rotational alignment with each other during pressing in the bore as when pressed together into said normal working configuration.

6. The method of claim 1, said step of forming a sleeve with a tapered inner surface including cold forming the inner surface on a die, said step of reducing the diameter of the combined button and sleeve including grinding the exterior surface of the sleeve to the desired diameter.

7. The method of claim 5, said step of .forming a sleeve with a tapered inner surface including cold form ing the inner surface on a die, said step of reducing the diameter of the combined button and sleeve including grinding the exterior surface of the sleeve to the desired diameter. Q

8. The method of claim 7 wherein the taper of said inner surface converges toward the end wall of the cylindrical bore and said step of pressing the button and sleeve together in the cylindrical bore includes first pressing until the sleeve rests against the end wallof the bore and second pressing until the button rests against the end wall of the bore.

9. The method of claim 7 wherein said taper of said sleeve inner surface diverges toward the end wall of the cylindrical bore and said step of pressing the .button and sleeve together in the cylindrical bore includes first pressing until the button rests'against the end wall of the bore and second pressing until the sleeve rests against the end wall of the bore.

10. A method of installing a button assembly having an externally tapered button and an internally tapered metal sleeve, in a cylindrical bore of a rock drillinghead assembly, said button assembly having an outer diameter slightly larger than the cylindrical bore, comprising;

forming a hollow metal sleeve having a tapered inner surface and an outer-surface, forming a solid button having a tapered outer surface of substantially the same shape as said sleeve ta pered inner surface, a working end surface and an abutment end surface, elastically expanding the hollow sleeve outside of the bore to a normal working position and, while expanded, shaping the outside of the sleeve to a desired interference fit diameter greater than the bore diameter, v relaxing the sleeve partially into an intermediate position to reduce the sleeve to a diameter less than the bore diameter, with the sleeve in said intermediate position, inserting said button and sleeve into said bore until the abutment end of the button engages the end of the bore, and moving the sleeve from said intermediate position into engagement with the end of the bore whereby the sleeve is expanded against the button and the bore to hold the button tightly within the bore. 11. A method of installing a button assembly having an externally tapered solid button and an internally tapered metal sleeve surrounding the button into a cylindrical bore of a drilling head assembly, said bore having side and end walls, comprising;

forming the sleeve to a desired size and shape with the outside of the sleeve being of a first size smaller than the bore side wall, placing the formed internally tapered sleeve and the solid button in said bore, and moving the internally tapered sleeve and button further relative to each other with a force which does not exceed the elastic limit of the sleeve while simultaneously radially elastically expanding the sleeve from said first'size to a second larger size in tight engagement with the bore sidewall so that the button is held tightly in the bore by the friction between the sleeve and the boresidewall. 12. The method of claim 11, said sleeve having a 'hardness of at least 3840 Re,

13. The method of claim 11, saidstep of moving the sleeve including pressing the sleeve until it seats against the end wall of the bore.

14, The method of claim 11, said step of forming the sleeve including expanding the inside of the sleeve to match the size and shape of the button outer surface, and forming the outer surface of the sleeve while expanded fully over the button outside of the bore to a shape corresponding to the shape of the sidewall of the bore and to a size exceeding the size of the sidewall of the bore by the desired interference fit, said step of placing the formed sleeve and the button in the bore including relaxing the sleeve to reduce its outer size to less than the size of the sidewall of the bore.

15. The method of claim 14, said step of forming the outer surface of the sleeve while expanded outside of the bore including pressing the sleeve over the button into a working configuration, said step of relaxing the sleeve including withdrawing the sleeve along the button from its working configuration.

16. The method of claim 15, said bore outer surface converging toward the outer end of the bore,

17. A method of installing an externally tapered button in a cylindrical bore of a drilling head, said bore having an inner end, a sidewall and an outer end, comprising;

forming a sleeve with an inside taper smaller than the external taper of the button by a first predetermined amount and forming the sleeve-with an outside diameter of a size which is smaller than the diameter of the sidewall of the bore by a second predetermined amount which is smaller than the said first predetermined amount, and v axially moving the internally tapered sleeve and button relative to one another in the bore so as to elastically radially stretch the sleeve by the button against the sidewall of the bore to an extent greater than said second predetermined amount and byta force that does not exceed the elastic limit of the sleeve, thereby retaining the combined button and sleeve in the bore by the friction between the sleeve and the side wall of the bore caused by the elastic compressive load in the sleeve and sidewall of the bore. I

18. The method of claim 17, said tapers of said button and sleeve converging toward the outer end of the bore.

19. The method of claim 17, said tapers of said button and sleeve diverging toward the outer end of the bore. 

1. A method of installing and holding an externally tapered button in a cylindrical bore in a drilling head by means of an internally tapered metal expansion sleeve, comprising; forming the sleeve with its outer surface oversized relative to the sidewall surface of the bore and with its inside surface generally the same shape as the tapered outer surface of the button and undersized relative thereto, axially pressing the sleeve and button together into a normal working relationship and, while in said relationship, shaping the outer surface of the sleeve to generally the same shape as the sidewall surface of the bore and to a size that is oversized relative to said sidewall surface while the sleeve and button are fully pressed together and that is undersized relative to said sidewall surface when the sleeve is in a relaxed state, less than fully pressed together, moving the button and sleeve relative to one another sufficiently to permit the sleeve to shrink to said undersize whereat its outer surface is small enough to permit the sleeve to enter the bore without interference and then pressing the button and internally tapered metal sleeve together in the cylindrical bore until the sleeve is elastically expanded by the button tightly between the button and the sidewall surface of the bore.
 2. The method of claim 1, said cylindrical bore having an inner seat said internally tapered metal sleeve being annular and having a generally cylindrical outer surface, said step of pressing the button and sleeve together in the bore including abutting the button against said inner seat.
 3. The method of claim 2, said seat including an inner end wall of the bore, the taper of said sleeve inner surface converging toward the end wall of the cylindrical bore and said step of pressing the button and sleeve together in the cylindrical bore including first pressing until the sleeve rests against The end wall of the bore and second pressing until the button rests against the end wall of the bore.
 4. The method of claim 2, said seat including an end wall of the bore, said taper of said sleeve inner surface diverging toward the end wall of the cylindrical bore and said step of pressing the button and sleeve together in the cylindrical bore including first pressing until the button rest aggainst the end wall of the bore and second pressing until the sleeve rests against the end wall of the bore.
 5. The method of claim 1 wherein said button and sleeve are in the same exact rotational alignment with each other during pressing in the bore as when pressed together into said normal working configuration.
 6. The method of claim 1, said step of forming a sleeve with a tapered inner surface including cold forming the inner surface on a die, said step of reducing the diameter of the combined button and sleeve including grinding the exterior surface of the sleeve to the desired diameter.
 7. The method of claim 5, said step of forming a sleeve with a tapered inner surface including cold forming the inner surface on a die, said step of reducing the diameter of the combined button and sleeve including grinding the exterior surface of the sleeve to the desired diameter.
 8. The method of claim 7 wherein the taper of said inner surface converges toward the end wall of the cylindrical bore and said step of pressing the button and sleeve together in the cylindrical bore includes first pressing until the sleeve rests against the end wall of the bore and second pressing until the button rests against the end wall of the bore.
 9. The method of claim 7 wherein said taper of said sleeve inner surface diverges toward the end wall of the cylindrical bore and said step of pressing the button and sleeve together in the cylindrical bore includes first pressing until the button rests against the end wall of the bore and second pressing until the sleeve rests against the end wall of the bore.
 10. A method of installing a button assembly having an externally tapered button and an internally tapered metal sleeve, in a cylindrical bore of a rock drillinghead assembly, said button assembly having an outer diameter slightly larger than the cylindrical bore, comprising; forming a hollow metal sleeve having a tapered inner surface and an outer surface, forming a solid button having a tapered outer surface of substantially the same shape as said sleeve tapered inner surface, a working end surface and an abutment end surface, elastically expanding the hollow sleeve outside of the bore to a normal working position and, while expanded, shaping the outside of the sleeve to a desired interference fit diameter greater than the bore diameter, relaxing the sleeve partially into an intermediate position to reduce the sleeve to a diameter less than the bore diameter, with the sleeve in said intermediate position, inserting said button and sleeve into said bore until the abutment end of the button engages the end of the bore, and moving the sleeve from said intermediate position into engagement with the end of the bore whereby the sleeve is expanded against the button and the bore to hold the button tightly within the bore.
 11. A method of installing a button assembly having an externally tapered solid button and an internally tapered metal sleeve surrounding the button into a cylindrical bore of a drilling head assembly, said bore having side and end walls, comprising; forming the sleeve to a desired size and shape with the outside of the sleeve being of a first size smaller than the bore side wall, placing the formed internally tapered sleeve and the solid button in said bore, and moving the internally tapered sleeve and button further relative to each other with a force which does not exceed the elastic limit of the sleeve while simultaneously radially elastically expanding the sleeve from said first size to a second larger size in tight engagemenT with the bore sidewall so that the button is held tightly in the bore by the friction between the sleeve and the bore sidewall.
 12. The method of claim 11, said sleeve having a hardness of at least 38'' 40 Rc.
 13. The method of claim 11, said step of moving the sleeve including pressing the sleeve until it seats against the end wall of the bore.
 14. The method of claim 11, said step of forming the sleeve including expanding the inside of the sleeve to match the size and shape of the button outer surface, and forming the outer surface of the sleeve while expanded fully over the button outside of the bore to a shape corresponding to the shape of the sidewall of the bore and to a size exceeding the size of the sidewall of the bore by the desired interference fit, said step of placing the formed sleeve and the button in the bore including relaxing the sleeve to reduce its outer size to less than the size of the sidewall of the bore.
 15. The method of claim 14, said step of forming the outer surface of the sleeve while expanded outside of the bore including pressing the sleeve over the button into a working configuration, said step of relaxing the sleeve including withdrawing the sleeve along the button from its working configuration.
 16. The method of claim 15, said bore outer surface converging toward the outer end of the bore.
 17. A method of installing an externally tapered button in a cylindrical bore of a drilling head, said bore having an inner end, a sidewall and an outer end, comprising; forming a sleeve with an inside taper smaller than the external taper of the button by a first predetermined amount and forming the sleeve with an outside diameter of a size which is smaller than the diameter of the sidewall of the bore by a second predetermined amount which is smaller than the said first predetermined amount, and axially moving the internally tapered sleeve and button relative to one another in the bore so as to elastically radially stretch the sleeve by the button against the sidewall of the bore to an extent greater than said second predetermined amount and by a force that does not exceed the elastic limit of the sleeve, thereby retaining the combined button and sleeve in the bore by the friction between the sleeve and the side wall of the bore caused by the elastic compressive load in the sleeve and sidewall of the bore.
 18. The method of claim 17, said tapers of said button and sleeve converging toward the outer end of the bore.
 19. The method of claim 17, said tapers of said button and sleeve diverging toward the outer end of the bore. 